Rotary index mechanisms

ABSTRACT

A counter has a ratchet wheel which can be indexed in either direction to add to or subtract from the count held. Indexing is by means of initially the appropriate one of two pawls, the final movement of any indexing step being by a common movable member. This allows identical and interchangeable pawls to be used for both addition and subtraction.

United States Patent 1191 1111 3,802,282 Cook Apr. 9, 1974 1 ROTARY INDEX MECHANISMS 2,841,119 7/1958 Hard 74/128 3,124,967 3/1964 Kull 74/142 [75] Inventor- John Hayward Cook 852,690 5/1907 Wright 74/128 Sawbndgeworth, England 1,126,084 1/1915 Reisbach 1 74/128 sign Numbering c s Sahlgren Limited, London, England I Primary ExaminerBenjamin W. Wyche [22] Filed Sept 1972 Assistant Examiner-Wesley S. Ratliff, Jr. [21] Appl. No.: 287,730 Attorney, Agent, or Firm-Brisebois & Kruger [30] Foreign Application Priority Data 57 ABSTRACT Oct 13. 1971 Great Brltain 47704/71 A counter has a ratchet Wheel which can be indexed 52] CL 74/128 in either direction to add to or subtract from the count [51] Int. Cl. 27/02 held Indexing is y means of initially the pp p [58] Field f i 142 one of two pawls, the final movement of any indexing step being by a common movable member. This allows 56] References Cited identical and interchangeable pawls to be used for both addition and subtraction. UNITED STATES PATENTS 3,526,149 9/1970 Wollar 74/142 9 Claims, 1 Drawing Figure p 52 5/ ii ROTARY INDEX MECHANISMS The present invention relates to rotary indexing mechanisms, and particularly to an improved indexing mechanism capable of providing indexing movement in both directions of rotation. The term indexing mechanism is used herein to refer to a device capable of providing an output movement in the form of discrete steps of a predetermined size; such steps may be rotary or linear, although the term is normally used to refer to a rotary mechanism.

Indexing mechanisms in general have many applications and are used, for example, in time pieces and in many applications where it is desired to control a rate of revolution of an output shaft, or to control the degree of rotation of an output shaft. One such application in which rotary indexing mechanisms are useful is in counting apparatus where an input movement of some sort, either linear or rotary, is transmitted into successive incremental rotational steps of an output shaft. The angle of rotation of the output shaft then provides an indication of the number of units of input movement received in a time interval between two successive observations of the angular position of the output shaft.

Such counters are well known, they utilise simple indexing mechanisms which provide an accurate output angular displacement of the output shaft for a range of different values of the input movement. This is essential for use as a counter since the output shaft must produce an indication of the number of separate input movements which is independent of the strength of the individual input movements. Although known simple indexing mechanisms are quite satisfactory in this respect they can only operate to provide indexing movement in one direction so that they cannot be used to provide a counter capable of subtracting as well as adding. More complex indexing mechanisms have been made which are capable of providing indexing movement in both directions. Such mechanisms, however, by virtue of being more complex, are more cumbersome and bulky than the simple unidirectional indexing mechanisms and the advantages of simplicity, ease of construction and reliability of the simple indexing mechanism are all to some extent lost. The present invention seeks to provide a simple bi-directional indexing mechanism in which the above mentioned advantages of simple indexing mechanisms are retained.

According, therefore, to the present invention there is provided a bi-directional rotary indexing mechanism comprising a ratchet wheel, two individually movable pawls each mounted so as to move the ratchet wheel in a respective different direction of rotation through part of an indexing step when the pawl makes an operative excursion from a rest position, and a third member mounted so that it is displaced when either pawl makes an operative excursion, and arranged to engage the ratchet wheel to complete the indexing step thereof as the pawl returns to its rest position.

It will be appreciated that embodiments of this invention can retain the simplicity and convenience of simple unidirectional indexing mechanisms since they only require a very small number of additional components. Manufacture of this invention can be simplified, moreover, if both pawls are made substantially identical. The pawls are then interchangeable. Preferably the two pawls are pivotally mounted and operated by respective slidably mounted operating members. Pivotally mounted pawls are particularly convenient and accurate since the mounting pin can be accurately and conveniently located.

ln a preferred embodiment of the invention which is particularly suitable for use in a counting device capable of addition and subtraction the two operating members are mounted for sliding movement substantially parallel to each other, operative movement of each being in the same direction. This arrangement is convenient in an electrically operated machine in which the input displacements are provided, for example, by means of respective solenoids, one for additive and one for subtractive movements, since the two solenoids can be identical and mounted side by side. Moreover, in such an arrangement the electrical signals energising each solenoid can, if desired, be of the same polarity, the selection of which input line to a solenoid determining the polarity of the indexing movement.

One embodiment of the invention will now be more particularly described, with reference to the accompanying drawing which is a diagrammatic plan view of the embodiment.

Referring now to the drawing there is shown an indexing mechanism generally indicated by the reference numeral 11, comprising a ratchet wheel 12, having a set of peripheral radial teeth 21, mounted for rotation with an output shaft 13 on a base member 14. Also mounted on the base meber 14 are two pawls l5 and 16 which are pivoted to the base member 14 by means of two pivot pins 17 and 18 respectively. The pawls l5 and 16 are shaped at their free ends 19 and 20 respectively to engage the peripheral teeth 21 of the ratchet wheel 12 when they are rotated about their respective pivot pins 17 and 18 towards the ratchet wheel 12.

Also mounted on the base 14, on either side of the ratchet wheel 12, there are two operating members 22 and 23. Each of these operating members 22, 23 is provided with a pin 24, respectively, extending transverse the plane of the base 14, that is parallel to the axis of the shaft 13 and the pivot pins 17 and 18. The pins 24 and 25 engage in co-operating slots 26 and 27 in the pawls l5 and 16 respectively.

The slots 26 and 27 are inclined with respect to the longitudinal axis of the operating members 22 and 23 which are mounted for sliding movement in the direction of their longitudinal axes. Thus, when an operating member such as the member 23 is moved to the right as shown in the drawing, the pin 25 engaged in the slot 27 causes the pawl 16 to rotate clockwise about the pin 18. The end 20 of the pawl 16 thus engages with one of the teeth 21 of the ratchet wheel 12 and moves it to cause the ratchet wheel 12 to rotate clockwise. When the operating member 23 is moved to the left of the position shown in the drawing, the pawl 16 is rotated anticlockwise away from the ratchet wheel 12 and the end 20 of the pawl 16 disengages from the wheel 12.

Between the two operating members 22 and 23 there is mounted a return pawl 28. The return pawl 28 is slidably mounted on the base 14 and guided to move in the direction of its longitudinal axis which is parallel to the longitudinal axes of the operating members 22 and 23 by means of two slots 29 and 30; the slot 29 engages around the shaft 13 and the slot 30 engages around a pin 31 which projects transverse the plane of the plate 14. The return pawl 28 is formed with two recesses 32 and 33 into which project two lugs 34 and 35 on the operating members 22 and 23 respectively. These lugs are so positioned, and the recesses 32 and 33 are of such a size that an operating movement of the operating member 22 or 23 will displace the return pawl 28 by the interengagement of the corresponding lug and recess, but the movement of the other recess on the return panel 28 with respect to the lug on the other operating member, (that is the operating member which is not making the operating movement), will not cause displacement of the other operating member by the engagement of the corresponding lug and recess.

The return pawl 28 is biased by means of a spring 36 towards the ratchet wheel 12, and is shaped at the part adjacent the ratchet wheel 12 with a pointed end to tooth 37 which corresponds to the shape of the side walls of the teeth 21, so that when the return pawl 28 is moved by the spring 36 into engagement with the ratchet wheel 12 the point or tooth 37 engages in the space between two adjacent teeth 21 and defines accurately the position of the ratchet wheel.

The indexing mechanism operates to provide an indexing rotation in either direction in a substantially identical manner. For example, in the rest position the return pawl 28 is biased towards an engagement of its pointed tooth 37 with a space between two adjacent teeth 2] on the ratchet wheel 12. In this position the pins 24 and 25 both hold the pawls l5, 16 away from the ratchet wheel 12. If the operating member 23, for example, is moved to the right by an actuating mechanism (not shown) which may, for example, comprise a solenoid operated by a pulse train from a suitable circuit, the pin 25 will move down the slot 27 and bias the pawl 16 to move towards the ratchet wheel 12 thereby rotating it in a clockwise direction by engagement of the pointed end of the pawl 20 with the side wall of one of the teeth 21. The movement of the operating member also causes the sliding movement of the return pawl 28 away from the ratchet wheel 12 against the biasing action of the spring 36 by virtue of the engagement of the lug 35 in the recess 33. When the pin reaches the right hand end of the slot 27 (the position shown in the drawing) the force moving the operating member 23 is removed and the operating member is urged towards its initial position by the return pawl 28 which is biased towards the ratchet wheel 12. The tooth 37 of the return pawl 28 engages with the side wall of one of the teeth 21 of the ratchet wheel 12 and completes the indexing step of the ratchet wheel 12 while at the same time the operating member 23 moves the pin 25 along the slot 27 to return the pawl 16 to its initial position.

It will be seen that indexing movement of the shaft 13 in the counter-clockwise direction is obtained in an exactly identical manner by operation of the pawl 15, the operating member 22, and the return pawl 28. This arrangement is particularly convenient since the return pawl 28 operates to provide the indexing location of the ratchet wheel 12 at the end of each indexing step to accurately position the ratchet wheel 12, and therefore the shaft 13, for both directions of rotation. Similarly manufacture is facilitated because the pawls 15 and 16 are identical and interchangeable, as are the operating members 22 and 23. The symmetry of the device lends it particular convenience particularly, for example, when used with electromechanical actuators such as solenoids which may be conveniently located side by side to receive signals to index the mechanism in one direction or the other. Such an arrangement may be found, for example, in counting devices where it is required to count a sequence of pulses and display the total as a rotation of a shaft carrying a number of indications such as by a digit wheel 38 fixed to the shaft 13 in the drawing, so that indexing rotation represents addition in one direction and subtraction in the other.

1 claim:

1. A bi-directional rotary indexing mechanism comprising a support, a ratchet wheel mounted for rotational indexing in the support, two alternatively movable pawls mounted to move the ratchet wheel in opposite directions of rotation through only the initial part of an indexing step when a pawl makes an operative excursion from a rest position, actuating means for causing a selected one of said pawls to, make an operative excursion initiating an indexing step, and a third member actuated by said actuating means to engage the ratchet wheel to complete an initiated indexing step as the actuated pawl returns to its rest position.

2. A bi-directional rotary indexing mechanism as claimed in claim 1 in which both pawls are substantially identical and said ratchet teeth are symmetrical.

3. A bi-directional rotary indexing mechanism as claimed in claim 1, in which the two pawls are pivotally mounted in the support and said actuating means comprises two slidably mounted operating members, each connected to actuate one of said pawls.

4. A bi-directional indexing mechanism as claimed in claim 3, in which the two operating members are mounted for sliding movement substantially parallel to each other, operative movement of each being in the same direction.

5. A bi-directional indexing mechanism as claimed in claim 4, in which the third member is slidably mounted for movement parallel to and between the said two operating members.

6. A bi-directional indexing mechanism as claimed in claim 1, including means for biasing said third member towards engagement with the ratchet wheel.

7. A bi-directional indexing mechanism as claimed in claim 6, in which the third member and the said two operating members have interengaging parts by means of which excursive movement of each of the operating members is transmitted to the third member, and return movement of the third member is transmitted to the corresponding operating member.

8. A bi-directional indexing mechanism as claimed in claim 1, in which an excursion of a pawl moves the ratchet wheel by approximately half of an indexing step, the step being completed by the third member as the pawl returns to its rest position.

9. A counting device having a bi-directional indexing mechanism as claimed in claim 1. 

1. A bi-directional rotary indexing mechanism comprising a support, a ratchet wheel mounted for rotational indexing in the support, two alternatively movable pawls mounted to move the ratchet wheel in opposite directions of rotation through only the initial part of an indexing step when a pawl makes an operative excursion from a rest position, actuating means for causing a selected one of said pawls to make an operative excursion initiating an indexing step, and a third member actuated by said actuating means to engage the ratchet wheel to complete an initiated indexing step as the actuated pawl returns to its rest position.
 2. A bi-directional rotary indexing mechanism as claimed in claim 1 in which both pawls are substantially identical and said ratchet teeth are symmetrical.
 3. A bi-directional rotary indexing mechanism as claimed in claim 1, in which the two pawls are pivotally mounted in the support and said actuating means comprises two slidably mounted operating members, each connected to actuate one of said pawls.
 4. A bi-directional indexing mechanism as claimed in claim 3, in which the two operating members are mounted for sliding movement substantially parallel to each other, operative movement of each being in the same direction.
 5. A bi-directional indexing mechanism as claimed in claim 4, in which the third member is slidably mounted for movement parallel to and between the said two operating members.
 6. A bi-directional indexing mechanism as claimed in claim 1, including means for biasing said third member towards engagement with the ratchet wheel.
 7. A bi-directional indexing mechanism as claimed in claim 6, in which the third member and the said two operating members have interengaging parts by means of which excursive movement of each of the operating members is transmitted to the third member, and return movement of the third member is transmitted to the corresponding operating member.
 8. A bi-directional indexing mechanism as claimed in claim 1, in which an excursion of a pawl moves the ratchet wheel by approximately half of an indexing step, the step being completed by the third member as the pawl returns to its rest position.
 9. A counting device having a bi-directional indexing mechanism as claimed in claim
 1. 